摘要:

The refractive index of a film of transparent or translucent material may be determined by immersing the film in a suitable liquid mixture and observing the intensity of light reflected from the surface of the specimen. The composition of the immersion liquid is varied, and a record is made of its refractive index (measured on a refractometer) and of the reflected light intensity. The refractive index of the film is the same as that of the immersion liquid giving the lowest reflected intensity. This has been confirmed by experiments with a glass plate, whose refractive index was known. According to Fresnel's laws of reflection, the experimental data should fit a parabola with its minimum at the refractive index of the film. On fitting the data by the method of least squares, the minimum is obtained with a standard deviation of the order of 0.002 refractive index units. The method has been applied to several plastic materials.

ISSN:0021-8979    

DOI:10.1063/1.1697671

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

A new method is presented for determining number average molecular weights of liquid polymers, by means of easily performed measurements. The molecular weight is an explicit functionM=Bdv13−An2−1n2+2of the sound velocityv, densityd, refractive indexn, and the two empirical constantsAandB. Accuracy of about 2 parts per hundred was attained for the lower polyethylene glycols. The method seems suitable for molecular weights up to several thousand. Sound velocities were measured by an acoustic interferometer, at one megacycle frequency.

ISSN:0021-8979    

DOI:10.1063/1.1697672

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

An instrument for shortening the time and labor required in constructing particle size histograms from electron micrographs is described. Representative histograms obtained with the instrument for GR‐S latices are shown. Linear, surface, and volume‐equivalent diameters of non‐spherical particles are defined, and variations in the instrument for plotting such diameters are proposed.

ISSN:0021-8979    

DOI:10.1063/1.1697673

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

It has been predicted theoretically that, in general, a right‐circular cylinder of incompressible, highly elastic material, which is isotropic in its undeformed state, cannot be held in a state of pure torsional deformation by means of a torsional couple alone. In addition, normal surface tractions must be exerted over the plane ends of the cylinder. These normal surface tractions depend on the amount of torsion and on position on the plane ends of the cylinder. Experiments are reported here in which this phenomenon is observed in a right‐circular cylinder of pure gum compound. The dependence of the surface traction on amount of torsion and its distribution over the surface of the cylinder is studied by measuring the bulging of the rubber into small holes in a metal plate on one end of the cylinder.

ISSN:0021-8979    

DOI:10.1063/1.1697674

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

The frequency and temperature dependence of the elastic losses of polyvinyl chlorides (0° to 80°C, 60 to 1400 c.p.s.) and of natural rubber and butadiene‐styrene copolymers (GRS) of different relative concentration (−50° to 35°C, 20 to 3500 c.p.s.) was studied by 3 methods, in which the motion of a reed in free or forced vibration is observed. Natural rubber at temperatures above 20°C, and polyvinyl chloride exhibit frequency independent losses, the mechanism of which is not yet clear. The results for rubber below 20° and for GRS can be explained by a relaxation theory. The behavior of the elastic losses also reflects the existence of a second‐order transition, below which rotation of chain segments is hampered.

ISSN:0021-8979    

DOI:10.1063/1.1697675

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Measurements have been made of the direct current conductivity of rubbers loaded with carbon black. Shawinigan and Continental R‐40 blacks compounded in natural rubber and GR‐S were studied, and the resistivities were determined as functions of time, temperature, concentration and elongation. Resistance decreased with time, at first very rapidly, then more slowly, approaching an equilibrium value. This behavior seems to be independent of the type of black used. Temperature coefficients of resistance (at 50°C) were positive for Shawinigan stocks, negative for samples containing R‐40, and tended to increase with increasing concentration of black and with increasing extension of the sample. At low concentrations, R‐40 gave higher conductance in GR‐S than did Shawinigan. At high loadings, Shawinigan gave the higher conductance in both GR‐S and natural rubber. Resistance increased with elongation for all stocks containing R‐40. The Shawinigan GR‐S samples showed an inversion; for small elongations the resistance increased on stretching, but for higher extensions the resistance decreased. The results are interpreted on the assumption that the carbon black tends to form chains in the rubber matrix.

ISSN:0021-8979    

DOI:10.1063/1.1697676

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

In the first paper of this series it was shown that for cork, held at constant compression, the stress as a function of compression, temperature, and time was separable into two factors, one factor representing the load‐compression curve and the other describing the decay of stress with time. In the present paper the dependence of the load‐compression curve upon temperature is studied. After the sample has relaxed at constant temperature and compression for a time sufficiently long so that the change of stress with time may be neglected, stress‐temperature curves were obtained. These curves showed a linear dependence of the stress upon the temperature. From the stress‐temperature curves the resolution of the stress into its additive components due to internal energy and entropy was carried out. The physical significance of this resolution is discussed. The experiments were carried out with a refined version of the apparatus described in the first paper. In particular, the apparatus was corrected for rate of thermal expansion.

ISSN:0021-8979    

DOI:10.1063/1.1697677

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Load‐compression curves were taken for natural cork. The S‐shape of the curves is discussed and a theoretical fit is made for the high end of the curve, assuming an initial stiffness and an incompressible part of the cork material. A comparison is made between repeated compressions, with and without a recovery period of time.Pressure‐volume curves were also taken and their significance discussed in connection with the load‐compression curves leading to an evaluation of Poisson's ratio.

ISSN:0021-8979    

DOI:10.1063/1.1697678

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

A cold cathode rectifier is described in which corona discharge is used at atmospheric and higher pressures in hydrogen and nitrogen free of electron‐attaching impurities. This kind of tube has advantages where the current demands upon a rectifier are small.

ISSN:0021-8979    

DOI:10.1063/1.1697679

出版商:AIP    

年代:1947

数据来源: AIP

摘要:

Two approximations are made in the solution of Reynolds' lubrication equation for the case of a finite slider. These approximations lead to a series of equations that are easy and rapid to use for flat sliders, and which are also applicable to curved sliders. Examples of their use are presented, and a number of calculations are made to determine the range of slider proportions to which they may be applied with sufficient accuracy. The method is of special value for wide sliders which are difficult or impossible to analyze by other methods.

ISSN:0021-8979    

DOI:10.1063/1.1697680

出版商:AIP    

年代:1947

数据来源: AIP